1. Field of the Invention
The present invention is related to the manufacture of fiberglass structures and, more particularly, is directed towards a novel method and apparatus which facilitates the manufacture of large, fiberglass structures and permits same to be accomplished with total operator safety.
2. Description of the Prior Art
Fiberglass tanks are presently widely used for the storage of liquids. In particular, extremely large fiberglass tanks, ranging in capacity from 2,000 to 12,000 gallons, are extremely popular in the underground storage of inflammable liquids, such as gasoline. Such tanks are commonly utilized in, for example, retail gasoline stations. It is important that such tanks be leak-proof, strong, corrosive resistant, and enable storage or large amounts of gasoline.
While the utilization of such large, underground fiberglass tanks has become extremely popular over the last twenty years or so, the technique for manufacturing such tanks has not progressed much beyond the initial, labor-intensive techniques first developed when the market for such tanks initially arose. Basically, the common manufacturing technique, still in use today, centers about the use of a smooth, revolving cylindrical mandrel of approximately eight feet in diameter. A workman is positioned adjacent the revolving mandrel and is equipped with a portable raw material applicator known in the art as a chopper gun. A chopper gun includes means for chopping fiberglass roving into small (1"-2") strands, a resin spray nozzle and a catalyst spray nozzle.The workman basically sprays the mixture onto the outside surface of the mandrel to form a smooth cylindrical, eight-foot diameter drum. Ribs are then physically placed about the circumference of the drum to provide added structural strength for the finished product. Such ribs are spaced along the entire length of the drum and normally consist of cardboard spacers and/or a lightweight plastic filler. Another layer of continuous woven roving is then bonded with the resin and catalyst onto the outer shell of the drum to secure the ribs and provide additional strength.
The hemispherical end caps for the cylindrical drum are generally formed in separate, horizontally positioned molds, and are again applied by hand-held chopper guns. Each end cap must then be bonded onto each end of the drum by hand using fiberglass mats, woven roving and resin. There frequently arises either fitting or bonding problems between the caps and the cylindrical drum, as a result of the inability to control the wall thickness of each product with any precision.
Problems with the technique described above revolve both around the finished product and the safety of the workmen. The finished product, whose dimensions are difficult to control from batch to batch, frequently experiences disjoining of the circumferential ribs. Further, as described above, the separately formed end caps are difficult to handle and install. Quite clearly, the entire process is hand labor intensive and, indeed, is quite messy. The workmen must wear disposable clothes due to the impregnation thereof by the raw materials being sprayed. Although masks are frequently required, they are seldom used. Ventilation is required but is not always adequate, which can result in the intoxication of the workers from the fumes of the raw materials. The admixture of raw materials drips and hardens on the floor and is quite difficult to clean up. Unfortunately, the quality of skilled labor available to perform the above-described technique is very low, as a result of the dangerous and difficult working conditions.
Several attempts have been made to overcome some of the conditions set forth above, but without much overall success. For example, others have used a segmented mold constructed of wood and/or plastic which is balanced on four wheels, one of which is motor driven to cause the mold to rotate. A forklift or similar vehicle has wooden planking attached thereto upon which one or two workmen would be positioned with their hand-held chopper guns. The platform is then positioned inside the mold, and the workmen spray the inside surface of the mold with their chopper guns as the mold rotates. Blower fans are aimed in the general direction of the inside of the mold in an effort to circulate enough air inside the mold to prevent asphyxiation of the workmen. The workmen may even be required to wear a mouthpiece respirator or "gas mask". When the finished product is formed, the mold is unfastened, and the product removed.
This technique, while providing some advantages over the first technique, still is quite dangerous to the workmen, and does not result in an overall uniform end product. For example, the only protection afforded the workmen while spraying inside the mold is their mouthpiece respirators and disposable coveralls. The workmen still find it difficult to breathe. In the event that the mold stops rotating, by virtue of a power outage or the like, prior to the solidifying of the fiberglass or plastic coating, the laminate on the inside wall of the mold could drip down onto the workmen. The working conditions are, to say the least, extremely hazardous. The mold itself, being constructed of wood and plastic, has a relatively short life expectancy, and frequently must be discarded after making one, two or three products. An entirely new mold would then have to be constructed at a considerable cost per product. The wall thickness of the fiberglass tank itself manufactured by such techniques is difficult to control, and the dimensions of the end product basically rely upon the "feel" of the worker.
In sum, the prior art techniques for constructing fiberglass tanks, or other large plastic or fiberglass structures, involve a lot of hand labor, are extremely inefficient, result in non-uniform end products, and are extremely dangerous to the workers.
Prior art U.S. Pat. Nos. of which I am aware which relate to this general area include: 2,513,289; 2,790,997; 2,945,531; 3,003,188; 3,150,219; 3,301,925; 3,381,744; 3,561,059, 3,679,337; 3,689,191; 3,744,951; 3,783,060; 3,822,980; 3,914,105; 3,957,410; 3,996,322; and Re. 25,587.